Ethanol enhances expression of cell surface class I major histocompatibility complex (MHC) antigens in a variety of cell lines; up to an eightfold increase is observed in an embryonic cell line. Increased cell surface expression, following alcohol treatment, occurs with a concomitant increase in steadystate RNA levels. This effect is promoter dependent and restricted. The effective ethanol concentration (1%) is physiologically attainable. Measurement of class I MHC antigen on peripheral blood lymphocytes in acutely ethanol intoxicated patients showed ahighly significant increase over controls.